By guest author Dr. Ilana Richman and Dr. Emma Samelson-Jones
Helen is a 59 year old woman with a history of alcohol use disorder in remission and hypertension. She presents with a new skin rash that started 4 weeks ago. It began as tiny bumps on her skin that came with a little “head” and then “opened up.” She first noticed the bumps after staying overnight in a hotel and believes they are caused by insect larvae under her skin. She brings in a small container that appears to have a dead insect and some flaky material that looks like pieces of skin or scab.
Helen has been reading online about insect infestations and reminds you that medical professionals often don’t believe patients. She continues to go to work, sleeps well, and denies auditory or visual hallucinations.
On mental status exam, she is alert and fully oriented. She is anxious and speaks rapidly. She is perseverative about insects but her thought process is not disorganized. On skin exam, she has numerous, clean-based, punched-out, linear lesions on her arms ranging from 5-15 mm in length and in various stages of healing, from eschar to hypopigmented areas. There are no lesions on her torso or between her fingers or toes.
CBC, CMP, TSH, Vitamin B12, and urine drug screen are unremarkable. Dermatology performs multiple skin biopsies; no parasites, scabies, or other organisms are identified. The histology is consistent with prurigo nodularis, a reaction pattern caused by chronic scratching. Helen is empirically treated for scabies with ivermectin and started on a topical steroid for prurigo nodularis.
Helen returns to see you 4 weeks later, concerned that the bugs are still burrowing in her skin. She is satisfied with the care provided by dermatology but continues to believe that her skin is infested. She reports poor sleep and persistent worry but denies depression or anhedonia. She has lost 8 lbs in one month from “all this stress”. Her skin exam is unchanged. You perform a full neuro exam, and it is unremarkable. She worries that clinicians will tell her she is “crazy.”
How do you support a patient with delusional infestation (DI)?
Delusional infestation (DI), previously called delusional parasitosis, is a condition in which patients experience persistent itching or crawling sensations and believe that they are infested with a pathogen (such as worms, mites, or insects) or inanimate material, despite the absence of objective medical evidence.
These sensations and the belief in infestation cause significant distress and may lead to a repeated self-examination, elaborate cleaning routines, and attempts to isolate and capture the perceived pathogen. These behaviors cause skin lesions that further reinforce a patient’s belief that they are infested. Patients usually seek help from primary care clinicians or dermatologists rather than psychiatrists.
DI is a somatic type of delusional disorder. Like other delusional disorders, it typically begins in middle or late adulthood. People with delusional disorder are not disorganized and may function well outside the context of the specific delusion. When hallucinations occur, they are related to the specific delusional belief.
How do you diagnose DI?
An international group of experts on DI convened by the European Society for Dermatology and Psychiatry published consensus recommendations on the definition, diagnosis, and management of DI in 2026 (Kemperman, 2026). The group recommended examining any materials brought in by the patient (e.g. specimens, photographs), as this may aid diagnosis and help build trust. A urine screen for substances should also be performed in all patients with suspected DI to assess for substance-related causes.
The group recommended blood tests to look for medical causes of DI, and neuroimaging in selected cases when neurologic disease is a concern. They did not recommend one universal laboratory workup; testing should be guided by the history, examination, and clinical context. They emphasized close collaboration among dermatologists, psychiatrists, and other relevant specialists in diagnosing and managing DI (Kemperman, 2026).
The UCSF psychodermatology clinic recently published a pragmatic approach to DI that recommends initial laboratory testing with CBC, CMP, TSH, Vitamin B12, and urine drug screen–consistent with the international recommendations (Leung, 2026). Consider head imaging in any adult with focal neurologic signs or symptoms, and any older adult with new onset psychosis, including DI.
How do you work with patients whose illness explanation differs from yours?
Patients may understand the cause of their symptoms differently from their clinicians. For example, a patient may say, “The problem is that environmental toxins have caused inflammation, and I need chelation therapy,” while the clinician believes the patient has lupus and needs urgent systemic steroids.
How do we form and maintain a therapeutic relationship with a patient who believes “the problem is the bugs,” when the medical evaluation suggests DI?
Most DI expert panelists recommended against naming the belief as a delusion. Instead, they favored symptom-focused language and communication strategies tailored to the patient’s level of insight and receptivity (Kemperman, 2026). Consider reviewing the “An approach to navigating chronic delusions” within this previous PsychSnap.
In particular, when a person holds a false belief with high conviction, there is nothing to be gained by directly challenging that belief. Instead, focus on shared concerns, such as distress, anxiety, sleep disruption, skin discomfort, or impaired functioning.
For example, if Helen asks if you believe she is infested, you could say:
“I feel confident that we have looked thoroughly for infestations and treated you for any infestations that could have been missed on biopsy. I am confident that your dermatology team is on the right track with the treatments they have offered for your skin. At the same time, this situation has caused you tremendous stress, to the point where you’re having trouble sleeping and are losing weight. I’d like to talk about treatment options that could help with the stress while you continue the treatments from dermatology.”
How do you treat DI?
The psychiatric condition of DI should be treated with antipsychotic medication concurrently with any co-occurring skin conditions as early as possible (Kemperman, 2026). As in schizophrenia, a longer duration of untreated psychosis in DI is associated with poorer outcomes (Lepping, 2024)
Evidence regarding the preferred first-line antipsychotic medication for DI is limited. However, a 2024 retrospective observational study of 156 patients with DI (mean age, 62 years; 59% women) treated at 2 specialist DI clinics in the UK compared treatment responses across antipsychotics. Among the antipsychotics medications available in the US, risperidone had the highest response rate: 57% of patients improved (compared with 36% taking quetiapine, 25% taking olanzapine, and 20% taking aripiprazole) (Tang, 2025).
We recommend starting risperidone at 0.5mg bedtime and increasing to 1mg after 1 week. If tolerated, continue to increase the dose by 0.5mg every 2 weeks to a target dose of 3-4mg bedtime (Leung, 2026). Let patients know that they should not expect a benefit until they reach the target dose. The titration is slow to improve tolerability.
For patients taking risperidone, monitor for:
- Extrapyramidal movement disorders, including parkinsonism (shuffling gait, masked facies, resting tremor), akathisia, dystonia, and tardive dyskinesia
- Metabolic syndrome, including weight gain, dyslipidemia, and hyperglycemia
- Hyperprolactinemia, including gynecomastia, sexual dysfunction, menstrual changes, and infertility
If a patient achieves near remission of their symptoms with an antipsychotic, continue at the same dose for 3-4 months. Then consider tapering by 0.5mg a month, pausing the taper if symptoms return (Leung, 2026).
How do you talk with patients with DI about antipsychotic medication?
People with DI, like those with medically unexplained symptoms, benefit when the treatment focus shifts from finding a definitive cure to improving function and quality of life (Beach, 2014). Offer antipsychotic medication to help relieve bothersome symptoms that both the patient and the clinician recognize, such as insomnia, anxiety, emotional distress, or feelings of hopelessness.
While DI experts did not recommend disclosing the DI diagnosis to patients initially, there was broad consensus that patients should always be informed when an antipsychotic medication is prescribed (Kemperman, 2026).
Back to Helen: You tell Helen that the stress caused by the situation with her skin is having a major impact on her health, as reflected in her anxiety, her insomnia, and unintentional weight loss. You explain that other patients with similar symptoms in similar situations have benefited from a medication called risperidone. Risperidone may help her with anxiety and sleep. You ask whether she is open to hearing more about it.
She says yes. You let Helen know that if she looks up risperidone, she will see that it is classified as an antipsychotic medication that is used to treat schizophrenia. You clarify that you are not diagnosing her with schizophrenia. You explain that medications in the antipsychotic class are also for other conditions and symptoms, including nausea, and problems with mood, anxiety, sleep, and obsessive thoughts.
You offer a trial of risperidone to help with her anxiety and sleep. You hope that when she is feeling less stressed, her weight will stabilize. It is also possible that she will spend less time thinking about the bugs. You can assess her response by monitoring how many hours a day she spends thinking about the infestation, and her ability to engage in valued work, relationships, and activities.
After Helen consents to a medication trial, you prescribe risperidone 0.5mg tablets, and use the diagnosis codes for skin rash, insomnia, and anxiety in the chart. Because patients may read their clinical notes, documenting delusional infestation in the chart too early can quickly undermine trust and reinforce patient’s fears of begin dismissed as “crazy.”
Guest author Ilana Richman, MD, MHS is a primary care physician, health services researcher, and assistant professor in General Internal Medicine at Yale.
Key Points
- Involve a multidisciplinary team including dermatology to fully evaluate patient concerns about infestations.
- Avoid directly challenging patients’ beliefs about infestation. Instead, focus on shared, symptom-based concerns—such as emotional distress, anxiety, or sleep disruption—that both the patient and clinician can acknowledge.
- If a patient with DI is reluctant to see a psychiatrist, consider starting risperidone to target distressing symptoms in primary care.
Related PsychSnaps:
“When a young adult is hearing voices and psychiatry is unavailable for months, how can you help? Part 2” Emma Samelson-Jones, Aug 2023.
“How do you navigate chronic delusions to provide effective medical care?” Emma Samelson-Jones, Feb 2024.
References:
Beach, S. R., Kroshinsky, D., & Kontos, N. (2014). Case 37-2014: A 35-Year-Old Woman with Suspected Mite Infestation. The New England Journal of Medicine, 371(22), 2115–2123.
Kemperman PMHJ, Vulink NCC, Feikema FE, Bewley A, Lepping P, Gkini M-A, et al. Consensus recommendations for the diagnosis and management of delusional infestation: A Delphi study. J Eur Acad Dermatol Venereol. 2026; 00: 1–9. https://doi.org/10.1111/jdv.70502
Leung, A., Koo, J. Managing Dermatologic Delusional Disorders: A US Psychodermatology Perspective for Clinicians. CNS Drugs 40, 1029–1036 (2026). https://doi.org/10.1007/s40263-026-01309-5
Nakamura M, Koo J. Drug-Induced Tactile Hallucinations Beyond Recreational Drugs. Am J Clin Dermatol. 2016 Dec;17(6):643-652. doi: 10.1007/s40257-016-0219-z. PMID: 27637620.
Tang, Paul K., et al. “Efficacy of antipsychotics in delusional infestation.” Journal of the European Academy of Dermatology and Venereology 39.4 (2025): 815-822.
Vulink, Nienke C. “Delusional infestation: state of the art.” Acta dermato-venereologica 96.217 (2016): 58-63.
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